docs: def get_logout_url(service):
      """Get the configured logout URL for a given service identifier, if any."""
      for backend in _get_backends():
          try:
              return backend.get_logout_url(service)
          except AttributeError:
              raise NotImplementedError("%s.%s.get_logout_url() not implemented" % (
                  backend.__class__.__module__, backend.__class__.__name__)
              )
      return None